How do you add non-standard attributes in the old app?
By clicking on the attributes of a device, and then adding them, or by adding them to an Osmand upload.
Can you provide a screen recording of an example?
In the old web app you mean? Is it still available on one of the demo servers?
Otherwise just add &MyAttrib=somevalue to an Osmand upload, and create a Route report for the device.
Yes, the old app is still available. You can switch to it from the login screen.
Can you provide a screenshot of a route report with a custom attribute. Because I don't think it was ever possible for web reports.
The old web app would list all the attributes of a device, including the non-standard ones we created ourselves concatenated as one string.
In the modern web app we can only choose among a fixed set of attributes it seems.